Method for determining the controller output for controlling fuel injection engines

ABSTRACT

A method for adjusting the torque in an internal combustion engine is introduced having the steps: determining a desired torque; determining an operating point from measured values for air charge and rpm; determining a standard torque for this operating point; determining a desired efficiency from standard torque and desired torque; determining the lambda corresponding to this efficiency; determining the fuel quantity from the corresponding lambda and the air charge derived from measurement quantities. The fuel quantity in combination with the air charge yields the corresponding lambda for realizing the desired torque.

FIELD OF THE INVENTION

The invention relates to the adjustment of a desired engine torque byappropriate computation of the actuating variables especially foradjusting the air supply and the fuel supply to the engine in an enginehaving gasoline direct injection.

BACKGROUND OF THE INVENTION

An important operating mode of an engine having gasoline directinjection is the approximately unthrottled operation with high airexcess. The air mass in the combustion chamber is then substantiallyconstant and the excess-air factor (lambda) as an index for thecomposition of the air/fuel mixture is determined by the injected fuelmass. The air mass in the combustion chamber, in combination with lambdaand the rpm n, determines the torque developed by the engine. At highair excess, the desired torque can be adjusted for the most part via avariation of the fuel quantity. The combustibility of the mixture withhigh air excess is achieved by a spatially non-homogeneous mixturedistribution. This mode of operation is characterized as stratifiedoperation. In contrast to stratified operation, the operation with ahomogeneous mixture distribution is without air excess or only with aslight air excess. The invention relates to the determination ofactuating quantities in dependence upon the requested torque duringstratified operation.

External requirements on the intake manifold pressure during stratifiedoperation affect the air charge. Such requirements result, for example,from the situation that the exhaust-gas return and the tank ventingrequire a certain pressure drop. The request which brings about thelowest intake manifold pressure is realized by a minimum selection andintervention into the throttle flap position.

If one leaves the fuel quantity, which is to be injected for a desiredtorque, unchanged, then lambda changes. This has unwanted torque changesas a consequence.

SUMMARY OF THE INVENTION

The task of the invention is to avoid the unwanted torque changes.

Advantageously, the determination of the actuating quantity “injectiontime” is supplemented by a determination of the actuating quantity ofthe air supply.

In this way, the further task is solved, namely, to obtain anappropriate adjustment of the fuel supply and air supply to the engineto realize a pregiven engine torque while considering a maximumpermissible value for the air number lambda.

This further task is solved by a supplemental limiting of the air supplyto maximum values. This limitation guarantees the reproducibleadjustment of low torques over a variation of injection pulsewidths.Without this limitation, an unwanted adjustment to too lean a mixturecan result which could present problems with respect to thecombustibility of the mixture and/or the exhaust-gas emissions.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, an embodiment of the invention will be explained withrespect to the figures.

FIG. 1 shows the technical background of the invention.

FIG. 2 discloses an embodiment of the invention in the form of functionblocks; and,

FIG. 3 defines the formation of the limiting of the air supply.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Reference numeral 1 in FIG. 1 represents the combustion chamber of acylinder of an internal combustion engine. The inflow of air to thecombustion chamber is controlled via an inlet valve 2. The air is drawnby suction via an intake manifold 3. The inducted air quantity can bevaried via a throttle flap 4 which is controlled by the controlapparatus 5. Signals as to the torque demand of the driver are suppliedto the control apparatus, for example, in accordance with the positionof an accelerator pedal 6; a signal as to the engine rpm (n) istransmitted to the control apparatus from an rpm transducer 7 and asignal is supplied as to the quantity ml of the inducted air by an airquantity sensor 8. The control apparatus 5 forms output signals fromthese signals and, if required, further input signals concerningadditional parameters of the engine such as intake air temperature andcoolant temperature. The output signals are for adjusting throttle flapangle alpha via an adjusting element 9 and for driving a fuel injectionvalve 10 via which fuel is metered into the combustion chamber of theengine. The throttle flap angle alpha and the injection pulsewidth tiare viewed in the context of the invention as essential actuatingvariables for realizing the desired torque and these actuating variablesare to be matched to each other. Furthermore, the control apparatuscontrols, if required, an exhaust-gas recirculation 11 and a tankventing 12 as well as other functions such as the ignition of theair/fuel mixture in the combustion chamber. The gas force, which resultsfrom the combustion, is converted by piston 13 and crank drive 14 into atorque.

FIG. 2 shows an embodiment of the invention. Block 2.1 defines acharacteristic field which is addressed via the rpm (n) and the relativeair charge rl. The relative air charge is referred to a maximum chargeof the combustion chamber with air and indicates, to a certain extent,the fraction of a maximum combustion chamber or cylinder charge. The aircharge is formed essentially from the signal ml. The relative charge rlformed from measured quantities and the rpm (n) define an operatingpoint of the engine. Torques are assigned to various operating pointswith the characteristic field 2.1 and the engine generates these torquesunder standard conditions at the various operating points.

Standard conditions are determined by specific values of influencequantities such as ignition angle, air number lambda, EGR rate, tankventing condition, et cetera. As a standard condition with respect tothe air number, lambda=1 is pertinent. As a standard condition withrespect to the ignition angle, that ignition angle can be defined atwhich the maximum possible torque is adjusted.

With respect to each influence quantity, an efficiency eta can bedefined as a ratio of the torque under standard conditions to the torquewhich is adjusted for an isolated change of the influence quantity.

For deviations of several influence quantities from their standardvalues, the product of the efficiencies yields the ratio of the standardtorque at the standard values of the influence quantity to the torque atthe deviating influence quantities.

Stated otherwise, desired torque/standard torque=product of theefficiencies. The division of the wanted or desired torque (which isdependent, for example, on the driver command) divided by the standardtorque (which is determined for the individual operating point) in block2.2 therefore supplies the product of all efficiencies.

The values of the influence quantities such as EGR rate, ignition angle,et cetera, are present in the control apparatus. For example, with theaid of stored characteristic lines, the corresponding efficiencies aredetermined. The formation of the product of the efficiencies of theknown influence quantities follows. These are all influence quantitiesexcept lambda.

The division of the product of all efficiencies by the product of theefficiencies of the known influence quantities in block 2.3 supplies thelambda efficiency etalam.

From this lambda efficiency etalam, the corresponding lambda isdetermined in block 2.4, for example, via a characteristic lineintervention.

For various lambda values, the characteristic line eta of lambda yieldsthe ratio of the standard torque at lambda=1 to the torque at otherlambda values.

Block 2.4 thereby supplies precisely that lambda value which must beadjusted in the combustion chamber in order to induce the desired torquein the actual operating point, which is defined by the air charge rl andthe rpm (n), for the known remaining influence quantities such asignition time point, EGR rate, et cetera. In this connection, inducinghere means the generation of the gaseous force which delivers thedesired torque via piston and crank drive.

This desired lambda value, in combination with the air charge rl of thecombustion chamber derived from measurement quantities, determines thefuel quantity which must be injected to generate the desired torque.

From this, a relative fuel mass can be determined in block 2.5 bydividing rl by the lambda desired value determined in dependence uponthe desired torque. This fuel mass is then converted into the specificinjection pulsewidth as an actuating quantity in the fuel path.

This embodiment makes possible an adjustment of the desired torque inthe substantially dethrottled stratified operation of the engine.

The supplement shown in FIG. 3 makes possible the appropriate adjustmentof fuel supply and air supply to the engine to realize a pregiven enginetorque while considering a maximum permissible value for the air numberlambda.

Without the last condition, it could happen that an unwanted adjustmenttakes place to a mixture which is too lean and which could bring with itproblems in the combustibility of the mixture and/or in the exhaust-gasemissions.

The above is so because the torque increases for a fixed lambda withincreasing cylinder charge. If a variable lambda is permitted, then acertain bandwidth of adjustable torques results for a fixed charge. Thebandwidth is pregiven by lambda limit values outside of which, forexample, the combustibility is not ensured.

For this reason, there is a minimum torque for each charge. If smallertorques are wanted, then this cannot any longer be realized exclusivelyvia an intervention into the fuel path. Rather, a reduction of thecharge is then absolutely necessary.

According to the invention, the appropriate air charge and fuel mass areadjusted which will supply this pregiven desired torque in stratifiedoperation for a specific pregiven desired torque while considering amaximum permissible lambda value.

The air charge can, for example, be adjusted via the throttle flapopening angle as an actuating variable, for example, in systems havingelectronically controlled throttle flaps (EGAS). The computation of thisactuating variable takes place in the so-called air path.

The fuel mass is, for example, adjusted via the variation of aninjection pulsewidth as an actuating variable. The computation of thisactuating variable takes place as shown above in the so-called fuelpath.

The actual adjustment of the engine torque takes place, as described,with the aid of the fuel path.

In the air path, and as a supplement, a limiting of the charge takesplace to values which correspond to torques which are adjustable via thefuel metering. Stated otherwise, in the air path, the cylinder charge islimited to a value which results from the maximum permissible lambda forthe desired torque.

This is shown in FIG. 3. In block 3.1, first the maximum permissiblelambda value lambda_zul is determined which can, for example, bedependent upon the rpm (n) and can therefore be determined, for example,from a characteristic line.

The corresponding lambda efficiency etalam is determined in block 3.2from this maximum permissible lambda.

For known remaining influence quantities, the product of allefficiencies for the maximum permissible lambda can be determined in theblock 3.3.

This product corresponds to the ratio of command or actual torque to thetorque under standard conditions as explained above. For this view,which proceeds from a maximum permissible lambda value, this actualtorque corresponds to the torque which is adjusted for the maximumpermissible lambda. This actual torque is assignable to the maximumpermissible lambda value and is generated in block 3.4 via a logiccoupling of the product of the efficiencies with the standard torquemade available by block 3.5.

A maximum cylinder charge rl=f(lambda_zul) can be clearly assigned tothis specific actual torque via a characteristic line intervention inblock 3.6. At this maximum cylinder charge, the specific actual torqueadjusts while assuming a maximum lambda, that is, a lambda at the leanoperating limit between mixtures which are just combustible and just nolonger combustible.

This air charge rl defines the upper charge limit below which thedesired torque can be realized alone by intervention in the fuel path.

This charge limit can be realized via a limiting of the opening angle ofthe throttle flap to a maximum value alpha_max in block 3.7.

What is claimed is:
 1. A method for adjusting the torque in an internal combustion engine to which an air charge is supplied, the method comprising the steps of: determining a desired torque; determining an operating point from measured values for said air charge and engine rpm; determining a standard torque for this operating point; determining a desired efficiency from said standard torque and a desired torque; determining the lambda corresponding to this efficiency; and, determining the fuel quantity from the corresponding lambda and the air charge derived from measurement quantities, which fuel quantity, in combination with the air charge, yields the corresponding lambda for realizing the desired torque.
 2. The method of claim 1, the method comprising the further steps of: determining the maximum permissible lambda value for a regular combustion; determining the corresponding lambda efficiency; determining the total efficiency as a product of all efficiencies of the remaining known influence quantities for the maximum permissible lambda; determining the actual torque which adjusts for the maximum permissible torque and the efficiencies while considering the standard torque; determining a maximum cylinder charge rl at this actual torque whereat this actual torque is adjusted while assuming a maximum lambda; determining a maximum throttle flap angle alpha_max for limiting the charge. 